Attention is drawn to the U.S. Pat. No. 3,610,755, U.S. Pat. No. 5,319,434.
To resolve the above mentioned object there is proposed a laser system which comprises a laser light source as well as an output/input coupler unit. Latter comprises a circulator with an input, with an output and with an output/input. Further there is provided a detector unit which has an input. The input of the circulator is operationally connected to an output of the laser light source whereas the output of the circulator is operationally connected to the input of the detector unit. The output/input of the circulator is operationally connected to transmitter and receiver optics. The addressed input, output and output/input of the circulator are optical fibres.
Thereby in one embodiment the transmitter and receiver optics are in one embodiment joined to a single laser output/input port.
Due to the fact that all the input, output and output/input to or from the circulator unit are conceived by optical fibre and downstream the addressed circulator, output and input laser light is guided in one common optical fibre, the addressed laser system is highly compact. Especially providing the output/input optical fibre allows to flexibly locate respective output/input laser optics, separate or as a common port, optimized with respect to space consumption at a respective device equipped with the laser system.
In one embodiment the laser system comprises a master-oscillator/power-amplifier laser arrangement.
In a further embodiment which clearly may be combined with the just addressed embodiment which comprises a master-oscillator/power-amplifier, the laser light source comprises a laser diode.
Thereby a further improvement with respect to compactness is achieved and, additionally, the possibility to generate relatively high power laser light.
In a further embodiment the laser light source is a pulsed laser light source. Thereby and with an eye on the output/input coupler unit as addressed above the overall laser system becomes most suited for distance measuring based on mutual evaluation of transmitted laser pulses and of received laser pulses.
In a further embodiment the laser system according to the present invention comprises an active optical fibre power-amplifier which has an input and an output. The input of such active optical fibre power-amplifier is operationally connected to the output of the laser light source whereas the output of the active optical fibre power-amplifier is operationally connected to the input of the circulator. By providing and construing the addressed amplifier by active optical fibre, on one hand relatively high power laser light is generated and on the other hand the requirement of constructional compactness is maintained.
In a further embodiment the just addressed active optical fibre power-amplifier is pumped.
Still in a further embodiment wherein the laser light source is pulsed the laser system additionally comprises an evaluation unit with an input which is operationally connected to an output of the detector unit. The evaluation unit performs evaluation on multiple laser pulses as detected. Thereby the evaluation accuracy is significantly improved as e.g. with respect to range measurement.
Still in a further embodiment the addressed active fibre power-amplifier is pumped by a pumping diode which further increases constructional compactness and positively affects power consumption of the overall laser system.
Still in a further embodiment the active fibre power-amplifier is gain-modulated.
Gain modulation of the addressed amplifier allows to cope with disturbing influences upon the laser system downstream the addressed amplifier which affect specific characteristics of laser light upstream the addressed amplifier. Instead of selectively remedying on the spot such disturbing entities downstream the amplifier, the addressed gain modulation generically allows to compensate for the respective negative impact on the characteristic of output laser light. In a further embodiment the active fibre power-amplifier is pumped and is gain-modulated by at least one of intensity of pumping light, spectrum of pumping light, pumping pulse width of pumping light, length of active fibre, spectral shift of an optical filter characteristic.
In a further embodiment which comprises on one hand the active fibre power-amplifier which is pumped by pulsing, and, on the other hand the addressed laser light source which generates pulsed laser light, pulsing of amplifier pumping is time-synchronized with the pulsed laser light. Thereby at the addressed pumping, additionally to a synchronized pumping component there may be provided a pumping component which is not synchronized but which provides for a possibly time-varying pumping signal bias.
In a further embodiment the addressed gain modulated active fibre amplifier acts as an adjusting member in a negative feedback control loop whereat a characteristic i.e. a physical entity as e.g. intensity or signal-to-noise ratio is senses in the output laser light as a measured value. This value to be controlled is compared with a desired value or with a desired time course of such value and the gain of the active fibre power-amplifier is adjusted in dependency of the result of such comparing.
Thereby and as was already addressed such a negative feedback control loop allows to achieve and to maintain a desired physical value or characteristic in the output laser light and to cope with disturbing entities within the laser system.
Because providing an active fibre optical amplifier as was addressed on one hand significantly rises output laser light power but on the other hand may introduce additional noise to the output laser light especially by amplified spontaneous emission ASE, in a further embodiment there is provided downstream the addressed amplifier an optical fibre filter which has a filter characteristic the spectral position of which being controllably shiftable.
Normally such optical fibre filter is selected to be a narrow pass-band filter which operates either in pass-band transmission or pass-band reflection. On one hand by such filter being construed as an optical fibre filter, the overall compactness of the laser system is substantially maintained. On the other hand by providing such filter the signal-to-noise ratio of laser light downstream the filter is improved. Additionally providing such filter with a filter characteristic which is shiftable with respect to spectral location, a possibility is introduced to cope with disturbing effects on the output laser light. If e.g. the spectral location of the spectral band of laser light as generated shifts e.g. due to aging or varying temperature, then provision of a spectrally fixed filter characteristic would lead to variation of the overall amplification. By controllably shifting the spectral position of the addressed filter characteristic so as to be matched with the shift of the addressed spectral band, the shift of the spectral band of the generated laser light may not affect the overall amplification. Without such a shiftable filter characteristic or, as was addressed, gain modulation, it would, as an example, be necessary to stabilize the temperature at the laser source by cooling or by means of a temperature negative feedback control loop. Such measures would substantially increase constructional efforts and space for the overall system as well as power consumption.
It is perfectly clear that the principal of providing a controllably shiftable filter characteristic may also be applied to the laser system according to the present invention without having an active fibre power-amplifier.
In a further embodiment the just addressed filter characteristic is shiftable with respect to its spectral location in dependency of a temperature. Thereby it becomes possible to cope with undesired variation of overall amplification which are e.g. due to spectral shift of the spectral band of laser light caused by variation of temperature. As the source which is most affected by temperature variation is the laser light source whereat a varying temperature leads to a spectral shift of the spectral range of laser light, in one embodiment the addressed temperature is selected to be dependent from a temperature of the laser source.
In a further embodiment with the addressed active fibre power-amplifier, there is provided a stabilizing optical fibre filter in the laser light source and a downstream optical fibre filter downstream the amplifier. Please return to the definition of a stabilizing filter. The stabilizing filter and the downstream filter are normally narrow pass-band filters. The filter characteristics of both these filters are controllably shiftable with respect to their spectral position whereby these spectral shifts are matched. Thereby the spectral location of the spectral band of laser light towards the amplifier is governed by the stabilizing filter characteristic and its spectral location whereas noise reduction especially of ASE is performed by the downstream filter. By matching the spectral positions of both filter characteristics e.g. again dependent on temperature, substantially no variation of overall amplification due to shifting of the spectral band of the laser light as generated is present.
In a further embodiment of the laser system according to the present invention all the fibres namely of the input, the output and the output/input of the addressed circulator are standard single-mode fibres at a wavelength of laser light from the laser light source.
In a further embodiment making use of the addressed standard single-mode fibres the transmitter and the receiver optics have the same apertures. Still in a further embodiment departing from making use of standard single-mode fibres, laser light from the laser source is guided in the core of the fibres at the input and at the output/input of the circulator and received laser light is guided in the core as well as in the cladding of fibres at the addressed output/input of the circulator and at the output of the circulator.
Thereby in a further embodiment the numerical apertures of the transmitter optics and of the receiver optics are selected different.
Still in a further embodiment the addressed fibres at the input, output and output/input of the circulator are multi-mode fibres.
Still in a further embodiment the addressed fibres at the input, output and output/input of the circulator are polarization maintaining fibres whereby the laser source generates polarized laser light.
In a further embodiment at least one of the addressed fibres at input, output and output/input of the circulator is of one of the following types: photonic crystal fibre, single-clad fibre, double-clad fibre.
Still in a further embodiment the addressed circulator is an un-polarizing circulator.
Still in a further embodiment at least one of the addressed fibres at the input, output and output/input of the circulator is fusion spliced to a respective fibre of the circulator.
Still in another embodiment laser light throughout the laser system is substantially exclusively guided in optical fibres.
In a further embodiment one end of the output/input fibre is operationally connected to a transmitter optic and to a receiver optic. In one embodiment these optics are formed by one bi-functional optic, in another embodiment as two separate units.
Thereby in one embodiment the addressed end determines the divergence of a laser beam transmitted by the transmitter optic. Thereby considerable saving of lenses is achieved which clearly reduce costs, improves compactness and robustness.
Under a further aspect of the invention a device with a laser system which accords with the laser system as was addressed is portable. Thereby such device in one embodiment is even handheld. In a further embodiment such device incorporates the addressed laser system in a range finder- or target designator unit. Dependent on system power the operating range is up to at least 1 km but up to at least 10 km for higher power systems.
Under a further aspect of the present invention there is proposed a method for producing a laser beam out of a transmitter optic which method comprises generating laser light in an optical fibre having an end coupled to the transmitter optic and further determining the divergence of the laser beam by the conception of the addressed fibre end.
With respect to possible conception techniques we refer to the detailed description.
Still under a further aspect of the present invention there is proposed a handheld device with a laser system which is a part of a laser range finder or target designator and which operates in the addressed ranges.
Attention is drawn on the fact that the content of the European application no. 05 000 669.1 dated Jan. 14, 2005 as well as the content of the European application no. 04 029 867.1 dated Dec. 16, 2004 upon which the present application resides with respect to priority, is considered as a part integrated by reference to the present disclosure.
The inventions under all their aspects and combinations shall now be exemplified by means of the following figures.